This invention relates to a wiper control device for a vehicle and, more particularly, to improvements in a wiper control device capable of accurately stopping wiper blades always at the lowermost position of a wiping range regardless of the rotating speed of a wiper motor.
A wiper control device for a conventional vehicle controls, as shown in FIGS. 1 and 2, the rotation of and the stopping position of a wiper motor 3 by journaling a cam plate 2 formed with an annular electrode 1 of a predetermined pattern making slidable contact with cam contacts a, b and c integrally at a motor shaft 4 of the wiper motor 3 and selectively isolating or contacting the cam contacts a, b and c from or with the electrode 1 in accordance with the rotating position of the cam plate 2. That is, when the wiper is stopped, the cam contacts a and b make contact with the projection 5 of the electrode 1 of the cam plate 2 as shown. When a wiper switch 7 is turned ON from the above state in the state that an ignition switch 6 is turned ON, an electric current will flow through the wiper motor 3 in a circuit of a battery 8, the ignition switch 6, the ON terminal of the wiper switch 7 and the motor 3, thereby rotating the wiper blades to wipe a window glass surface. If the wiper switch 7 is turned OFF in the course of wiping the window glass, since the cam contacts a and c make contact and thus shortcircuits in the course of wiping the window glass, the current continues to flow thrugh the wiper motor 3 in a circuit of the battery 8, the ignition switch 6, the cam contact c, the cam contact a, the OFF terminal of the wiper switch 7 and the wiper motor 3 irrespective of the OFF state of the wiper switch 7. When the wiper blades then reach the lower end position of the wiping range, the cutout 9 of the annular electrode 1 arrives at the lower part of the cam contact c, the shortcircuit between the cam contacts a and c is thus opened, and the current of the wiper motor 3 is interrupted in this manner. However, the wiper motor 3 continuously rotates due to the inertia of rotation. When the projection 5 of the electrode 1 thus makes contact with the cam contacts a and b, the wiper motor 3 is shortcircuited in a closed loop formed by a circuit of the wiper motor 3, the OFF terminal of the wiper switch 7, the cam contact a, the cam contact b, and the wiper motor 3, and an electromagnetic brake action occurs to stop the wiper motor.
Since the wiper motor 3 will however stop in the conventional wiper control device after it rotates at a certain sliding angle due to the inertia of rotation as evident from the above described operation, the wiper motor 3 will irregularly stop at the position in accordance with the magnitude of the inertia and hence the magnitude of the actual rotating speed of the wiper motor 3, and it is accordingly impossible to always stop accurately at the correct middle line X--X position corresponding to the lowermost position of the wiping range in FIG. 2. Thus, if the wiper motor 3 does not stop at the correct middle line X--X position, the wiper blades on the window glass surface will stop above the position from the lowermost position of the wiping range. The wiper blades thus stopped disturb the visual field of a driver and accordingly cause difficulty in the safety of the vehicle.